Dinitrogen oxide or laughing gas (N2O) substantially contributes to the greenhouse effect and has a high Global Warming Potential (the extent to which a molecule contributes to the greenhouse effect in comparison with a molecule of CO2). A policy to reduce the emission of greenhouse gases has been developed in the past few years. Various important sources of N2O emission have been identified: farming, the industrial production of the precursors of nylon (adipic acid and caprolactam), the production of nitric acid, and motor vehicles fitted with a three-way catalyst.
Different catalytic and non-catalytic techniques can be used to make laughing gas harmless. Various catalysts are known for example for the catalytic decomposition or conversion of N2O into N2 and O2 (for example JP Application No. Hei-06-154611, which describes catalysts on a carrier basis, with transition metals and noble metals). However, this reaction with catalysts as claimed in the prior art is greatly inhibited by the presence of oxygen and water, which occur in the waste gases of virtually all the N2O sources mentioned above.
Another example is described in WO 2005/110582. This document describes a method for the catalytic decomposition of N2O in an N2O-containing gas in the presence of a catalyst, where the catalyst contains a zeolite that is loaded with a first metal chosen from a group of noble metals comprising ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold, and with a second metal chosen from a group of transition metals comprising chromium, manganese, iron cobalt, nickel and copper, and in which method the loading of the zeolite with metals is effected by loading the zeolite first with the noble metal and then with the transition metal.
Selective catalytic reduction is a promising alternative. Various catalysts are known from the literature for the reaction of N2O with reducing agents such as alkenes (CnH2n), alcohols or ammonia. The addition of saturated hydrocarbons (CnH2n+2) is technically and economically preferred to the use of the reducing agents mentioned above. Natural gas (CH4) and LPG (a mixture of C3H8 and C4H10) are attractive in this connection.